feat: use hq- prefix for Mayor and Deacon session names

Town-level services (Mayor, Deacon) now use hq- prefix instead of gt-:
- hq-mayor (was gt-mayor)
- hq-deacon (was gt-deacon)

This distinguishes town-level sessions from rig-level sessions which
continue to use gt- prefix (gt-gastown-witness, gt-gastown-crew-max, etc).

Changes:
- session.MayorSessionName() returns "hq-mayor"
- session.DeaconSessionName() returns "hq-deacon"
- ParseSessionName() handles both hq- and gt- prefixes
- categorizeSession() handles both prefixes
- categorizeSessions() accepts both prefixes
- Updated all tests and documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/statusline_test.go

@@ -30,9 +30,9 @@ func TestCategorizeSessionRig(t *testing.T) {
 		// Edge cases
 		{"gt-a-b", "a"}, // minimum valid
 
-		// Town-level agents (no rig)
-		{"gt-mayor", ""},
-		{"gt-deacon", ""},
+		// Town-level agents (no rig, use hq- prefix)
+		{"hq-mayor", ""},
+		{"hq-deacon", ""},
 	}
 
 	for _, tt := range tests {
@@ -67,9 +67,9 @@ func TestCategorizeSessionType(t *testing.T) {
 		{"gt-gastown-crew-max", AgentCrew},
 		{"gt-myrig-crew-user", AgentCrew},
 
-		// Town-level agents
-		{"gt-mayor", AgentMayor},
-		{"gt-deacon", AgentDeacon},
+		// Town-level agents (hq- prefix)
+		{"hq-mayor", AgentMayor},
+		{"hq-deacon", AgentDeacon},
 	}
 
 	for _, tt := range tests {